In 1969, the Army Corps of Engineers accomplished an awesome feat: They turned off Niagara Falls. They did it to clean up the area, and check for structural integrity. Here are pictures of this bizarre episode in structural engineering history.

For six months in the winter and fall of 1969, Niagara's American Falls were "de-watered", as the Army Corps of Engineers conducted a geological survey of the falls' rock face, concerned that it was becoming destabilized by erosion. During the interim study period, the dried riverbed and shale was drip-irrigated, like some mineral garden in a tender establishment period, by long pipes stretched across the gap, to maintain a sufficient and stabilizing level of moisture. For a portion of that period, while workers cleaned the former river-bottom of unwanted mosses and drilled test-cores in search of instabilities, a temporary walkway was installed a mere twenty feet from the edge of the dry falls, and tourists were able to explore this otherwise inaccessible and hostile landscape.